3,887 research outputs found

    Present status on experimental search for pentaquarks

    Full text link
    It has been ten years since the first report for a positive strangeness pentaquark-like baryon state. However the existence of the pentaquark state is still controversial. Some contradictions between the experiments are unsolved. In this paper we review the experimental search for the pentaquark candidates Θ+\Theta^+, Θ++\Theta^{++}, Ξžβˆ’βˆ’\Xi^{--}, Θc0\Theta_c^0 and Nβˆ—N^* in details. We review the experiments with positive results and compare the experiments with similar conditions but opposite results.Comment: 20 latex pages, 2 figures, to appear in IJMPA as a revie

    Transverse single-spin asymmetries of pion production in semi-inclusive DIS at subleading twist

    Full text link
    We study the single-spin asymmetries with the sin⁑ϕS\sin\phi_S and sin⁑(2Ο•hβˆ’Ο•S)\sin(2\phi_h -\phi_S) angular dependences for charged and neutral pions produced in semi-inclusive deep inelastic scattering on the transversely polarized proton target. The theoretical interpretations of the two asymmetries are presented in terms of the convolution of the twist-3 quark transverse momentum dependent distributions and twist-2 fragmentation functions. Specifically, we investigate the role of the distributions fTf_T, hTh_T and hTβŠ₯h_T^\perp in the sin⁑ϕS\sin\phi_S asymmetry, as well as the role of the distributions fTβŠ₯f_T^\perp, hTh_T and hTβŠ₯h_T^\perp in the sin⁑(2Ο•hβˆ’Ο•S)\sin(2\phi_h -\phi_S) asymmetry. We calculate these distributions in a spectator-diquark model and predict the corresponding asymmetries for the first time, considering the kinematics at HERMES, JLab and COMPASS. The numerical estimates show that the asymmetries are sizable, and the dominant contribution to the sin⁑ϕS\sin\phi_S asymmetry comes from the T-odd distribution fTf_T, while fTβŠ₯f_T^\perp gives the main contribution to the sin⁑(2Ο•hβˆ’Ο•S)\sin(2\phi_h -\phi_S) asymmetry. The future measurements on these asymmetries can shed light on the information of twist-3 transverse momentum dependent distributions.Comment: 11 pages, 12 figures, version published in PR

    Electron-nuclear entanglement in the cold lithium gas

    Full text link
    We study the ground-state entanglement and thermal entanglement in the hyperfine interaction of the lithium atom. We give the relationship between the entanglement and both temperature and external magnetic fields.Comment: 7 pages, 3 figure

    Pareto Navigation Gradient Descent: a First-Order Algorithm for Optimization in Pareto Set

    Full text link
    Many modern machine learning applications, such as multi-task learning, require finding optimal model parameters to trade-off multiple objective functions that may conflict with each other. The notion of the Pareto set allows us to focus on the set of (often infinite number of) models that cannot be strictly improved. But it does not provide an actionable procedure for picking one or a few special models to return to practical users. In this paper, we consider \emph{optimization in Pareto set (OPT-in-Pareto)}, the problem of finding Pareto models that optimize an extra reference criterion function within the Pareto set. This function can either encode a specific preference from the users, or represent a generic diversity measure for obtaining a set of diversified Pareto models that are representative of the whole Pareto set. Unfortunately, despite being a highly useful framework, efficient algorithms for OPT-in-Pareto have been largely missing, especially for large-scale, non-convex, and non-linear objectives in deep learning. A naive approach is to apply Riemannian manifold gradient descent on the Pareto set, which yields a high computational cost due to the need for eigen-calculation of Hessian matrices. We propose a first-order algorithm that approximately solves OPT-in-Pareto using only gradient information, with both high practical efficiency and theoretically guaranteed convergence property. Empirically, we demonstrate that our method works efficiently for a variety of challenging multi-task-related problems

    Establishing low-lying doubly charmed baryons

    Full text link
    We systematically study the SS-wave doubly charmed baryons using the method of QCD sum rules. Our results suggest that the Ξcc++\Xi_{cc}^{++} recently observed by LHCb can be well identified as the SS-wave Ξcc\Xi_{cc} state of JP=1/2+J^P = 1/2^+. We study its relevant Ωcc\Omega_{cc} state, whose mass is predicted to be around 3.7 GeV. We also systematically study the PP-wave doubly charmed baryons, whose masses are predicted to be around 4.1 GeV. Especially, there can be several excited doubly charmed baryons in this energy region, and we suggest to search for them in order to study the fine structure of the strong interaction.Comment: 6 pages, 2 figures, 1 table; A mistake was found when evaluating decay constants of the S-wave charmed baryons. The conclusion is not change
    • …
    corecore